A physical quantity sensor such as acceleration sensor and angular velocity sensor having a sensor chip mounted face down on a substrate is known (refer to, for example, JP-A-9-219423).
Using a face down mounting method, the mounting area of the chip can be reduced and the sensor size can be decreased correspondingly.
The inventor has advanced the development of a physical quantity sensor having a sensor chip and a circuit chip for processing signals from the sensor chip. In the physical quantity sensor, the sensor chip and the circuit chip are stacked in order to reduce the mounting area so that the manufacturing cost is reduced.
On the basis of a technical idea disclosed in JP-A-9-219423, the inventor has adopted the face down mounting method to develop a sensor having stacked chips and has made a prototype of the sensor.
FIG. 6A is a schematic plan view showing the prototype, and FIG. 6B is a schematic cross sectional view showing the prototype.
A package 100 is composed of multiple layers of alumina or the like. A wiring (not shown) is formed on the surface of the package 100 and inside the package 100. Through the wiring, the sensor can be electrically connected to an external circuit.
A sensor chip 200 detects physical quantity (mechanical quantity) such as acceleration, angular velocity, and pressure. The sensor chip 200 can be constructed, for example, by forming a diaphragm and movable parts on a semiconductor substrate. A circuit chip 300 is a signal-processing chip for the sensor chip 200. The circuit chip 300 is typically constructed as an integrated circuit (IC) chip.
As shown in FIG. 6B, the sensor chip 200 and the circuit chip 300 are stacked and bonded through bumps 500. The stacked body of the chip 200 and the chip 300 is mounted face down on the package 100 through the bumps 500 formed around the periphery of the circuit chip 300.
Since the bumps 500 have high stiffness, unwanted external vibrations are transmitted to the sensor chip 200 through the bumps 500 without being weakened. Therefore, the package 100 requires an external system such as a rubber pad for reducing vibration.
As described above, although the package 100 can be minimized, a rubber pad for vibration damping is attached around the package 100 in practical use as a sensor. Consequently, the whole size of the sensor including the rubber pad becomes larger and size advantage of the package 100 cannot be exploited.